Adventures of an Aviatrix, in which a pilot travels the skies and the treacherous career path of Canadian commercial aviation, gaining knowledge and experience without losing her step, her licence, or her sense of humour.

Thursday, September 01, 2011

Morse Numbers

Morse Code numbers are easy. You can tell when the signal you're hearing is a number, because they are all five segments long, and no letter has more than four segments. And unlike the letters, the numbers follow a perfectly logical pattern.

It's as if the five dashes are five blanks into which you enter the numbers: one dot for one and incrementing up to five dots for five, at which point the dots become the blanks and you start counting dashes. If you're expecting letters you start hearing a one and you think " E, no A, no W, no J, ah 1." With two it's "E, no I, no U, but by the fourth dash it's revealed to be 2. You also know on the fourth dash for 3, but all the others you have to wait until the end to know for sure.

I can't read Morse code as in to hear a message that is being broadcast to me. I use it only to verify. I want to verify the XT beacon, so I think, "X, that's _.._ and T is _" then I listen to make sure that's what I hear. It does leave me open to hearing what I expect, but that's not a situation that changes whether or not you have your eyes on the symbolic representation on the chart. I think it improves safety to be able to be watching my VOR needle while listening to the identifier for the next beacon.

That's all I have to say about that, but I know I have some readers far more knowledgeable on the subject than I, and I anticipate some informative comments from them.

8 comments:

Nothing to add, Aviatrix. Your hints seem like a good idea for someone wanting to verify a beacon code.

I would not recommend them for someone wanting to become fluent in receiving Morse code. Fluency requires the automatic association of the sounds with letters; mnemonics don't achieve that.

However, I can't think of any compelling reason that a pilot should put in the long hours of practice it takes to becoming fluent in the Morse code, unless she's run out of more useful things pilot things to study, or unless she wants to become an amateur radio operator.

I became fluent with morse courtesy of the Air force, back in the day when it was deemed a necessary skill to have when the teletype failed. Never used it in anger though.Learning was by rote, endless listening and writing down. Sending was much the same, but cadence was stressed as important in sending a readable signal. Speed not so much, with either a conventional key or a bug.

And unlike the letters, the numbers follow a perfectly logical pattern.

Morse code has a pattern for the letters as well, in making the shortest code(s) for the most frequent of letter(s), hence E being a single dot. I always thought Morse designed that, but wikipedia tells me it was someone named Alfred Vail.

If you're expecting letters you start hearing a one and you think " E, no A, no W, no J, ah 1."

To "read" Morse code like that takes far too much attention. It's a lot less work to wait for the entire letter/number to be heard and analyze it once at the end.

I pretty much agree with Wayne about not needing fluency in order to read slow-speed nav beacon IDs. But I think the first step of recognizing individual letters as a single rhythmic sound is still a good goal.

What speed are beacon idents sent at? The Aviatrix method will work up to about 5 words per minute (roughly a character every two seconds) but much beyond that Wayne Conrad's "automatic association of the sounds with letters (and numbers)" is needed.

I originally learned Morse by the traditional"dots and dashes" method - A is dot-dash, B is dash-dot-dot-dot and so on. But I only achieved fluency when I unlearned all that and learned the rhythm of the letters.

FAR 171.261 (7) The signal must be transmitted at a speed corresponding to approximately seven words per minute, and must be repeated at approximately equal intervals, not less than six times per minute, during which time the localizer is available for operational use.

Sarah's chart reminds me of Huffman, not Gray, code except that in Morse there is a separate symbol (a 3-dit gap) between letters so nodes in the body of the tree can be labelled as well.

In Huffman encoding the symbols are self terminating; you don't need the inter-letter gaps but no letter is represented by an initial sub-sequence of another letter in the way that they are in Morse, e.g., N (-.) is the same as the start of C (-.-.).